Electron discharge tube



Oct. 20, 1931. S. RUBEN ELECTRON DISCHARGE TUBE Filed July 11, 1927 Jwvcn o L SAMUEL RUBEN 5 5 hm Gno 141 5a,

\20 of an oxide coated tube.

35 field modulation effects.

Patented Oct. 20, 1931 Uurrizn STATES PATENT OFFICE SAMUEL. RUBEN, OF NEW YORK, N'. Y., ASSIGNOR TO RUBEN TUBE COMPANY, A COR- PORATION OF DELAWARE ELECTRON DISCHARGE TUBE Application filed: July 11, 1-927; Serial No. 205,024.

This invention relates. to an electron discharge tube and particularly it relates to an electron discharge tube having an indirectly heated electron emission element. Its object is the provision of a thermionic discharge device adapted tofunction when the emission element is heated by conduction from an element through which a heating current is conducted, with practically no interruption of the electron stream due to the cycles of a heating current.

In devices of this kind in the prior art two general types of cathode elements are employed: those dependent upon conduction from the heater element through an electrical insulating body or cover to the emitting surface, and those employing thermal radiation from an incandescent'filament to the adjacent emission element, usually in the form In both devices there is an appreciable thermal lag in the response from the emitter surface when the tube is connected in the heater circuit.

In the tube of my invention the elements employed reduce the lag factor toa negligible value, and the tube functions with substantially no hum.

To accomplish this result, for the heater element I use a conductor of low electrical resistance, such as a tungsten wire with a cross section so large that the current cycles have little response in thermal variation, and that only a low voltage is required for operation; this signifies low transverse electrical Upon the low resistance element is helically wound a relatively high resistance element, such as tantalum wire or a compound of nickel and chr0- mium', through which, because of its higher Jo specific resistance and the high contact resistance of the tantalum wire, a very small amount of the heating current is conducted, this element, however, having a high thermal conduction. For the electron emission ele- .45 ment is preferably employed a high emission sion element in this form is wound as a helixabout the high and low resistance elements, but contacting only with the latter element, with which. it contacts tangentially. The coated platinum wire is preferred because of its low operating temperature.

I find that the high resistance wire around the heater base is substantially the electrical equivalent of the insulation shells of lava or quartz of the devices of the prior art, but lacking the thermal lag of the latter due to its high thermal conductivity.

To provide for minimum potentialdilferences along the emitter, this element wound as described, about the other elements, is tapped at a point substantially equidistant from the ends, along the long axis of the assembled heater-cathode elements instead of the end, for its connection in the cathodeanode circuit. I

For a better understandingof the invention reference is made to. the accompanying drawings, illustrative of one embodiment thereof, in which, 1 shows the cathode with its several members, Fig. 2 represents a diagrammatic view of an evacuated tube containing a cathode and its several members, a grid and an anode, together with the connecting electricalcircuits, and Fig. 3 represents a plan section of the tube at 33. Fig. 4 is a detail view of the elements illustrated by Fig. 1. In the several figures the corresponding elements are represented by the same numerals.

Referring more particularly to Fig. 1, 1 represents a tungsten wire heater element, having helically wound around its tantalum wire 2 and helically wound over the latter the emitter, a thorated' tungsten wire 3, 3., rep resenting a lead from the emitter to the external cathode-anode circuit. Referring more particularly to Fig. 2, the heater element 1 is supported by conducting wires 1 1 and 1 connected by terminals 1 and 1,, through transformer T in the circuit of gen 95 eratorG. Tantalum wire is not connected in. any circuit, serving only asan electrical resistance between the heater and emitter elements and. as a thermal conductor to contacting emitter 3, which is wound upon the 100 tantalum wire, through which a negligible amount of the heating current is conducted to the emitter. The latter is connected by lead 3 and support 3,, by terminal 3 in the cathode-anode circuit in which are potential sources B and telephone receiver R. Mounted on the supports 4,, and 4 is grid 4 having a terminal at 4 for connection in the input circuit, in which I represents the input coil. Surrounding the cylindrical grid 4, is anode plate 5, shown partly cut away, mounted on supports 5. and 5 the former connected by terminal 5, in the cathode-anode circuit.

The operation of a tube having these elements is the same as that of the commonly known three-element vacuum tube, except that the filament is heated to emission temperature by conduction from a distinct heater element. There is practically no noticeable hum in the receiving circuit due to the cycles of any alternating current heating current.

High resistance materials, other than those named as composing the body separating the emitter from the heater, may be satisfactorily used. For instance, in this capacity such electrically conductive yet high resistance materials as carbon, graphite or a mixture of cotton and colloidal silver can be so employed. The mixture of cotton and colloidal silver should first be heated to convert the cotton into carbon, this combination having a fair thermal conduction and a high electrical resistance. The emitter may also satisfactorily be cylindrical in forrn WHatI'cIaini is? sank-vii. Jixse 1. A vacuum tube having an anode, a grid, a heater element composed of a refractory metal, an electrically conductive metal body wound upon and in surface contact with and having a relatively higher specific resistance than the heater element, and a metal cathode of relatively higher electron emissivity wound upon and in surface contact with the high resistance body.

2. A vacuum tube having an anode, a grid, a heater element for the direct conduction therethrough of a heating current, an electrically conducting metal body in surface contact with and having a relatively higher specific resistance and thermal conductivity tlan the heater element and an indirectly heated metal electron emission element wound upon and in tangential contact with the hi her resistance body, said emission element ing connected with the anode by a lead from a point along the long axis of the emission element between its two ends.

3. A vacuum tube having an anode, a grid, a heater element composed of tun sten and anelectrically conductive metal body in surface contact with and having a relatively higher specific resistance than the heater element, and an indirectly heated cathode wound upon and tangentially in contact with the higher resistance body, and connected from a point along the long axis of the emission element between its ends with the anode.

4. A vacuum tube having an anode, a grid and a cathode, the latter comprising a heater element, a tantalum body wound upon and in surface contact with the heater element and another metal body of relatively higher emissivity wound upon and tangentially in surface contact with the tantalum body.

5. A vacuum tube having an anode, a grid and a cathode, the latter comprising a heater element composed of tungsten, wound upon a tantalum body in surface contact with the heater element and another metal body of relatively higher emissivity wound upon and tangentially in surface contact with the tantalum body,

Signed at the city of New York in the county of New York and State of New York this 8th day of July, A. D. 1927.

SAMUEL RUBEN.

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